We have demonstrated InP/InGaAs/InP MBE-grown DHBTs fabricated with patterned sub-collector by elevated temperature 200 degrees C N+ implant and subsequent device material over growth. F-t/F-max > 250 GHz/300 GHz were obtained on DHBTs with 0.35 mu m x 6 mu m emitters from this process. Ring oscillators fabricated with this process showed good uniformity with 82% of yield on wafers and an average gate delay of 8 ps. Difference of surface morphology on re-grown DHBT layers over elevated temperature implanted and room temperature 22 degrees C implanted sub-collector was observed. (c) 2005 Elsevier Ltd. All rights reserved.